In recent years, for the purpose of reducing environmental loads, strict regulations against exhaust gases have been successively introduced in the automotive industry. The exhaust gases contain, in addition to carbon dioxide (CO2) as a global warming substance, various harmful substances such as particular matters (PM), hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). Among these substances, very strict regulation values have been imposed on PM and NOx. As the measure for reducing an amount of these substances discharged, gasoline automobiles are provided with a three-way catalyst, whereas diesel automobiles are provided with a diesel particulate filter (DPF). The exhaust gases are cleaned by passing through these members, and then discharged into atmospheric air.
In recent years, it has recently reported that the active sites of the three-way catalyst tend to be poisoned with phosphorus components in engine oils to thereby cause deterioration in a catalyst performance thereof, and that ash derived from metal components is deposited on the DPF to thereby reduce the service life of the DPF. At present, in the ILSAC Standard and the JASO Standard as standards for engine oils, the upper limits of the phosphorus content and ash content in engine oils have been established, and the engine oils having lower contents of these substances have now been developed.
There has been proposed addition of an aminoalcohol-based compound to a lubricating oil as an ashless detergent-dispersant (Patent Document 1).
However, since the aminoalcohol-based compound additive for lubricating oil disclosed in Patent Document 1 has unsatisfactory detergency at high temperature, an additional metallic detergent must be used. When such a metallic detergent is used so as to enhance high-temperature detergency, filter structures of exhaust gas cleaning apparatuses; e.g., a particulate trap and an oxidation catalyst for oxidizing unburnt fuel and lubricating oil, tend to be clogged (plugged) with deposits (metallic and other deposits), thereby problematically impairing characteristics of internal combustion engines.